1. Field of the Invention
The present invention relates to an electromagnetic device such as a motor or the like, for example, used in a transmission case containing oil.
2. Description of the Related Art
FIG. 4 is a plan view of the stepping motor 1. FIG. 5 is a sectional view of the stepping motor 1 shown in FIG. 4 along a line V—V. FIG. 6 is a sectional view of the stepping motor 1 shown in FIG. 5 along a line VI—VI. FIG. 7 is a sectional view of the stepping motor 1 shown in FIG. 5 along a line VII—VII. FIG. 8 is a perspective view of a critical portion of the stepping motor 1 shown in FIG. 4.
In the drawings, the permanent-magnet-type stepping motor 1, provided in a transmission case (not shown) containing oil, includes a resin casing 2, a resin cylindrical housing 12 connected with the casing 2, a motor body 3 received in the casing 2, a shaft 4 to be rotated by the motor body 3, and a converting structure for converting the rotational movement of the shaft 4 into linear movement. The casing 2 and the housing 12 form a cover.
In the drawings, the permanent-magnet-type stepping motor 1, provided in a transmission case (not shown) containing oil, includes a resin casing 2, a resin cylindrical housing 12 connected with the casing 2, a motor body 3 received in the casing 2, a shaft 4 to be rotated by the motor body 3, and a converting structure 31 for converting the rotational movement of the shaft 4 into linear movement. The casing 2 and the housing 12 form a cover.
The housing 12 is fixed at a first end thereof to the casing 2 by a plurality of screws 12A extending parallel to the shaft 4. The casing 2 is provided with a circular mating hole 2a formed therein, and the housing 12 is provided with a mating member 12a so as to be inserted in the mating hole 2a. In FIG. 6, the mating member 12a is provided with three positioning-protrusions 12b at the outer periphery of the mating member 12a, the positioning protrusions 12b protruding in the radial directions and in contact with the inner periphery of the mating hole 2a. The housing 12 is provided with an annular groove 12c formed therein at a face in connection with the casing 2.
The housing 12 is provided therein with a housing through-hole 12d communicating between the outside and the inside of the housing 12, the housing through-hole 12d being provided at a side face of the housing 12. A filter 13 for capturing contamination of oil is provided in the housing through-hole 12d. The shaft 4 is rotatably supported by bearings 14 and 15. The bearing 15 affixed in the housing 15 is a rubber-seal-type bearing.
The housing 12 is provided, at a second end thereof opposite to the first end fixed to the casing 2, with a rod 16 which reciprocates along the axis of the shaft 4 with the rotation of the shaft 4. The rod 16 is inserted into the housing 12 at the base end of the rod 16, and the other end of the rod 16 protrudes from the second end of the housing 12. The rod 16 is provided therein with a through-hole 16a communicating between the inside of the housing 12 and the inside of the rod 16. The housing 12 is provided at the inner face of the second end thereof with a sleeve 17 for guiding the rod 16 linearly moving, an oil seal 18 for avoiding contamination to penetrate from the outer periphery of the rod 16, and an annular stopper 19 for restricting the linear movement of the rod 16. The converting structure 31 includes a threaded part 4a of the shaft 4, a resin guide member 20 disposed at the base end of the rod 16 and coupled with the threaded part 4a, and a metallic stopper 21 for restricting the linear movement of the rod 16 at the other side of the annular stopper 19. The guide member 20 and the stopper 21 include stopper faces 20b and 21a, respectively, perpendicular to the rotational axis of the shaft 4. In FIG. 7, the guide member 20 is provided with rotation-restricting protrusions 20a for restricting rotation of the rod 16 formed extending in the radial directions at the outer periphery of the guide member 20. With this arrangement, the guide member 20 is moved in the axial direction of the shaft 4 by the rotation thereof. The rod 16 is mounted with a resin member 22 to be coupled with the first link 101 at the end opposite to the base end of the rod 16.
In the stepping motor 1 having the above-described configuration, when electrical current is applied to the coil 7 via the connectors 25, a rotation-driving magnetic field is generated in the coil 7, thereby rotating the rotor 6 and the shaft 4 as a unit. The shaft 4 is coupled with the guide member 20 at the threaded part 4a of the shaft 4, and the rotational movement of the guide member 20 is restricted, whereby the rotational movement of the shaft 4 is converted into the linear movement of the guide member 20 and the rod 16.
By the linear movement of the rod 16 in both directions, the transmission control valve (not shown) is opened and closed, whereby the ratio of rotational speeds between the driving shaft and the engine shaft varies, as described above.
Since a known stepping motor 1 is used in oil containing sulfur and sulfur compounds, an outer coating of a conductor is damaged by being caused by a fact described below, then a chemical reaction is generated between the sulfur and sulfur compounds and a copper wire of the conductor at a position in which the outer coating of the conductor is damaged, whereby copper of the copper wire dissolves due to the potential gradient between the adjacent copper wires, thereby causing short circuits or disconnection.                (A) When flashes are formed on a bobbin 50, large molding pressure is applied to a motor body 3 when a housing 12 is molded by an injection mold, whereby an outer coating of a conductor is damaged due to the flashes.        (B) When a coil 7 is formed by winding the conductor around the bobbin 50, the outer coating of the conductor is damaged by friction between the bobbin 50 and the conductor.        (C) After the conductor is wound around the bobbin 50, the conductor is adhered to the bobbin with the outer coating being thermowelded on the bobbin 50. Thereafter, the outer coating of the conductor is damaged by a thermal stress generated by the difference of materials between the bobbin 50 and the outer coating.        (D) When the thickness of the outer coating of the conductor is smaller than the size of the flash, a tip of the flash reaches the conductor when the conductor is wound around the bobbin 50, thereby damaging the outer coating of the conductor.        